The present invention relates to a shift control method and apparatus for an automatic transmission, and more particularly, to a shift control method and apparatus able to secure a stable shift response and minimize shift shock when the acceleration pedal is frequently depressed.
Generally, an automatic transmission performs gear shifting according to vehicle speed, throttle opening angle and the like by controlling hydraulic pressure through a plurality of solenoid valves. That is, if it is determined that a specific shift condition is satisfied, hydraulic pressure supplied from an oil pump is controlled according to a solenoid valve duty control so that a specific friction element of the transmission is activated to cause the gear shift to occur.
Automatic transmissions have some problems in that torque fluctuations are inevitable due to their intrinsic structure, and gear shift performance becomes worse as engine output and engine speed become high. It is difficult to solve such problems by controlling only the automatic transmission, and therefore, recently, engine control has come to be simultaneously performed with the automatic transmission control.
Frequent acceleration pedal depression is often inevitable because of road conditions and traffic conditions, and consequently a downshift also frequently occurs. According to one prior art attempt at a solution, in which engine speed is compared with turbine speed to minimize shift shock during downshift, the throttle opening rate is controlled to be lower than a target throttle opening rate if the engine speed is lower than the turbine speed. If the engine speed becomes higher than the turbine speed, the throttle opening rate is controlled to be the target throttle opening rate. However, when the acceleration pedal is frequently depressed, only engine control is performed, without transmission control. Consequently, a stable shift feeling cannot be secured, and shift shock frequently occurs.
The present invention provides an automatic transmission control method and apparatus that secures a stable shift feeling and minimizes shift shock by controlling the transmission in combination with ECU (Electronic Control Unit) control of the engine based on engine speed and turbine speed.
One embodiment of the present invention comprises an ECU communicating and cooperating with a TCU (transmission control unit). Preferably, the ECU controls generation of a throttle compensation control flag indicative of whether a shift delay is needed. The ECU also controls sending of the generated throttle compensation control flag to the TCU, when the throttle opening rate is controlled in such a way that the throttle opening rate is not proportional to the depression of the acceleration pedal. The TCU controls delay of a gear shift for a predetermined shift delay time period if it is determined that the shift delay is needed by reading the transmitted throttle compensation control flag. The TCU further controls performance of the gear shift.
According to a preferred embodiment, the ECU control preferably comprises: determining whether the throttle compensation control flag is equal to 1; determining whether an engine speed is lower than a turbine speed if it is determined that the throttle compensation control flag is not equal to 1; determining whether a throttle opening rate is greater than a predetermined throttle opening rate if it is determined that the engine speed is lower than the turbine speed; determining whether an amount of change in the throttle opening rate is greater than a predetermined amount of change in the throttle opening rate if it is determined that the throttle opening rate is greater than the predetermined throttle opening rate; and setting the throttle compensation control flag as 1 and transmitting the throttle compensation control flag to the TCU if it is determined that the amount of change in the throttle opening rate is greater than a predetermined amount of change in the throttle opening rate.
According to another preferred embodiment, the TCU control preferably comprises: determining whether the transmitted throttle compensation control flag is equal to 1; determining whether the shift is under way if it is determined that the transmitted compensation control flag is equal to 1; delaying the shift for the predetermined shift delay time period if it is determined that the shift is under way; and performing the shift by outputting a shift signal and resetting the throttle compensation control flag.
According to yet another preferred embodiment, the present invention provides a shift control method for an automatic transmission comprising: determining on the basis of an engine speed, a turbine speed and a throttle opening rate whether predetermined shift delay conditions are satisfied; delaying a gear shift for a predetermined time period if it is determined that the predetermined shift conditions are satisfied; and performing a gear shift.